In percussion rock drilling, impact pulses are provided to a tool by a percussion device in a rock drilling machine, whereby the drill bits at the outermost end of the tool penetrate the rock and break it. At the same time, the tool is pressed by means of a feeding device against the rock in such a manner that the contact between the tool and the rock remains and an as large proportion of the impact energy as possible is transmitted to the rock. Further, so as to provide effective impacts, the tool should be indexed by means of a rotating device between the impacts in such a manner that the drill bits hit a new location with every impact. The detached rock material is flushed away from the drill hole with a suitable medium. Percussion rock drilling thus has four sub-processes of drilling: percussion, feed, rotation and flushing. Drilling variables, in turn, include percussion power, impact energy, impact frequency, feeding power, feeding rate, rotating rate, rotating torque, flushing flow and flushing pressure. By adjusting the drilling variables, it is possible to affect the sub-processes of drilling and the efficiency of drilling.
Publication EP 0,112,810 discloses the adjustment of percussion power to achieve a maximum penetration rate. In the disclosed solution, the striking rate and impact frequency of a percussion piston are adjusted independently, which is possible in very few rock drilling machines, since it requires the adjustment of the stroke length. In typical pressure medium-operated percussion devices, the length of the stroke is constant and only the impact pressure and flow can be adjusted, and any changes made in them simultaneously affect both the striking rate and impact frequency. Further, a drawback with the solution described in the EP publication is that the control of drilling is only directed to adjusting the percussion power. As is known in the field, rock drilling is, however, a complex process, and to effectively control it in the manner described in the EP publication, by adjusting only one drilling variable, is not possible.